CORROSION INHIBITORS

Abstract: Ether polycarboxylic or polysulphonic acids are used as corrosion inhibitors in water treatment and coating compositions.

Description: cαRRosicw IMHTOΓPORS The present invention relates to corrosion inhibitors for use in water treatment and in anticorrosive paints, and for the surface treatment of metals, e.g. prior to coating, storage or metal finishing treatment. Corrosion of metals, especially by aqueous systems, is a major problem in virtually all manufacturing industries and also most service industries, institutions and homes. The problem is especially iiiportant in areas such as engineering, metal coating and finishing, chemicals and the oil industry as well as in domestic and institutional heating systems and in the building and construction industries and in transport. Corrosion inhibitors are typically compounds which can be added to water systems in very low concentrations, often referred to as threshold levels, e.g. in the range 2 to 200 ppm to inhibit the corrosion of metal surfaces. Classical corrosion inhibitors were based on polyvalent metals such as zinc and chromium. Environmental pressures have led to demands that such metals be replaced. Certain phosphonates, polycarboxylates and phosphono carboxylates have been found to exhibit corrosion inhibiting properties. However all suffer from disadvantages, including cost, chemical incompatibility with other components of the water system, low level of effectiveness and/or effectiveness restricted to particular ranges of pH. For example some prior art corrosion inhibitors are not effective in hard water, e.g. in the presence of calcium ions, some are rendered ineffective by chlorinating agents which may be used to sterilise water systems and most operate effectively only within certain narrowly defined pH ranges. Examples of known corrosion inhibitors include the water soluble salts of polymaleic acid, acetodiphosphonic acid and phosphono carboxylic and phosphonopolycarboxylic acids. Exartples of the latter are described in EP-A-0491391. Of the above compounds polymaleic acid gives a relatively low level of protection while the others contain phosphorus which some users prefer to avoid. Many of the above compounds have been used in water treatment and in particular in treating cooling water, boiler water, oil well injection water and in central heating systems. Another major application of corrosion inhibitors is in anti-corrosive paints, and similar coating compositions. Corrosion inhibitors may also be used to treat metal surfaces prior to storage or as part of a coating or metal finishing operation. We have now discovered that ether polycarboxylic or polysulphonic acids and their salts are very effective corrosion inhibitors. Ether polycarboxylic or polysulphonic acids or their salts may be obtained by reacting coπpounds containing a polyalkyleneoxy chain with an unsaturated carboxylic or sulphonic acid or its salts, e.g. in the presence of a catalyst such as a free radical initiator. One method of preparing ether polycarboxylate salts is described British Application No. 9314297-6. Alkyl ether polycarboxylic acids were described in EP 0 129 328 and WO 9000538, as acid stable surfactants. We have further discovered that ether polycarboxylic acids may be reacted with polyvalent metal bases to form water insoluble pigments which are of value in paints and other coating compositions for anticorrosive applications. The invention provides the use of ether polycarboxylic or polysulphonic acids and their salts as corrosion inhibitors in water treatment. According to a further embodiment the invention provides a method of treating aqueous systems liable to give rise to problems of corroding metal surfaces, which comprises adding thereto threshold levels of an ether polycarboxylic or polysulphonic acid or its water soluble salts. According to a third embodiment the invention provides the use of ether polycarboxylates or polysulphonates in anticorrosive coating conpositions. According to a fourth embodiment the invention provides an anticorrosive coating formulation comprising: a liquid vehicle comprising water, a volatile organic solvent and/or a drying oil; a binder which coirprises said drying oil and/or a resin dissolved or dispersed in said liquid vehicle; corrosion inhibitor dissolved or dispersed in said liquid vehicle; and optionally a pigment or dye dispersed or dissolved in said liquid vehicle; characterised in that said corrosion inhibitor coirprises an ether polycarboxylate or polysulphonate. According to a fifth embodiment our invention provides the use of ether polycarboxylates or polysulphonates to treat metal surfaces prior to coating or metal finishing operations or to storage. According to a sixth embodiment the invention provides a method for the treatment of metal surfaces which coirprises :- contacting said surfaces with an aqueous solution of an ether polycarboxylate or polysulphonate and subsequently subjecting said surfaces to at least one coating or metal finishing operation, greasing and/or storage. According to a seventh embodiment our invention provides an anticorrosive pigment comprising a polyvalent metal salt of an ether polycarboxylic acid or polysulphonic acid. According to an eighth embodiment our invention provides a coating cαrtposition having a polyvalent metal salt of an ether polycarboxylate suspended or dispersed therein. The ether polycarboxylates may be any of those disclosed in the aforesaid British Application No. 93 14297-6 the disclosure of which is incorporated herein by reference. For example the inhibitor may be a polycarboxylated or polysulphonated polyalkoxylate of general formula: 2 3 RCR 1 ), R (R ) Z H R ^ in which R is a straight or branched chain alkyl, alkaryl or alkenyl group or straight or branched chain alkyl or alkenyl carboxy group, having, in each case, up to 27, typically from 6 to 25 carbon atoms, or hydrogen, each an OC H or OC H,- 1 to 4, preferably , each other R group being a C -C alkyl, hydroxy alkyl or carboxyalkyl 4 group or, preferably H, R is OH, SO A, SO A, OR, sulphosuccinyl, C * 7 C 7 OCH CO A, or R NR , R is a C -C alkyl or hydroxyalkyl group, R is a C alkyl group, a benzyl group, a CH CO A, -> 0 or PO A group, A is a cation capable of forming water soluble salts of said carboxylic acid such as an alkali metal or alkaline earth metal, each z is from 1 to 5 preferably 1, y is at least 1 and (x+y) has an average value of from 1 1 2 to 50, wherein the R and R groups may be arranged randomly or in any order along the polyalkoxylate chain. 4 It is possible for R,R together to constitute a single divalent organic groups thereby providing a cyclic compound or to constitute a covalent bond thereby providing a crown ether. The compounds may be prepared by reacting (i) a compound of the formula 1 4 . 1 4 R(R ) R wherein R, R and R are as hereinbefore defined with (ii) a water soluble salt of an unsaturated carboxylic, polycarboxylic 5 5 sulphonic or polysulphonic acid C(R )_C(R ) as defined above, in aqueous solution in the presence of a free radical initiator, at a temperature sufficient to produce said polycarboxylate or polysulphonate. Polyalkoxylates (i) which can be carboxylated to provide corrosion inhibitors suitable for use according to the present invention are those having an alkoxylated chain with an average value of between 1 and 50 alkoxy units, preferably between 1 and 50 ethoxy and/or propoxy units. Preferred are polyethoxylates such as polyethylene glycol or less preferably polyethylene/polypropylene glycol copolymers containing up to 40% molar of propylene oxy residues, e.g. 0 to 20% molar. The polyalkyleneoxy chain may be terminated at one or both ends by organic or inorganic groups, including C to , preferably C to C , alkyl or alkenyl groups or alkyl or alkenyl carboxy groups (R- or RCO-) or alkylaryl groups including alkylphenyl groups, alkylene carboxylate [ (CH ) CO A] groups, a sulphosuccinyl group, glycoside, polyglycoside, alkyl glycoside or alkyl polyglycoside residues including fructoside or glucoside residues, or alkyl glucoside residues, sorbitan, sorbitan ester, glyceride residues including mono or di fatty acid glyceride residues (e.g. ROCH CHOHCH - or ROCH ROCH CH ) , sulphate groups, phosphono, phosphate or phosphate ester groups, amino groups including trialkyl ammonium (e.g. di C to alkyl such as dimethyl mono C , alkyl ammonium) , dialkyl benzylammonium (e.g. di C to alkyl such as dimethyl benzyl), dialkyl amine oxide, (e.g. di C to alkyl such as dimethylamine oxide) dialkylglycine (e.g. di C alkyl such as dimethyl glycine) and alkyl aminomethylene groups, as in ethoxylated ethanolamides e.g. ethoxylated coconut ono-or di-ethanolamide. Suitable polyalkoxylates, for use as (i) therefore include those of 1 4 general formula : R(R ) R 1 4 Wherein R,R and R are as hereinbefore defined, and y has an average value of from 1-50. In particular they include fatty alcohol alkoxylates, fatty acid alkoxylates, alkylphenyl alkoxylates, fatty acid alkylolamide ethoxylates, including ethoxylated mono and dialkylolamides, alkoxylated quaternary ammonium salts for example ethoxylated amine oxides and ethoxylated betaines and alkyl polyethoxy sulphates and sulphonates. Alternatively (i) may be a cyclic compound such as a crown ether e.g. a cyclopolyethyleneoxide having from 4 to 12 ethylene oxide groups. The polyalkoxylate(i) is reacted with a carboxylate or sulphonate (ii) in which the cation A is usually sodium, but may also be potassium or a sodium/potassium mixture. Other alkali metals such as lithium, rubidium or caesium are technically operable but unlikely to be selected on economic grounds. A may alternatively or additionally comprise ammonium or an amine such as isopropylamine or mono, di or triethanolamine or methyl pyridinium or quinolinium or magnesium. Alkaline earth metals such as zinc, magnesium and calcium may be useful, at least as part of the total A groups. Where reagents (i) and (ii) both comprise acidic groups, the counter-ions A may be the same or different. For water insoluble pigments it is preferred that at least the majority of A should be polyvalent metal such as zinc, magnesium, aluminium or calcium. The carboxylate or sulphonate (ii) may be added preferably as the sodium or potassium salt or alternatively the salt may be generated in situ by the neutralisation of the appropriate acid with a suitable amount of an acid neutralising agent, e.g. an alkali metal or alkaline earth metal hydroxide. The unsaturated carboxylate or sulphonate is preferably a salt of an unsaturated di- or poly-carboxylic or sulphonic acid. Preferably the double bond is adjacent to at least one carboxy1 or sulphonyl group. We prefer that the carboxylate or sulphonate has less than six e.g. 3 to 5 carbon atoms. The preferred carboxylate is maleate. Other suitable carboxylates include fumarate, aerylate, itaconate, methacr late, crotonate, isocrotonate, angelate, tiglate, and mesaconate. Suitable sulphonates include vinyl sulphonate. The proportion of carboxylate or sulphonate (ii) may conveniently be in the range of from 0.2:1 to 5:1 molar, based on the number of moles of alkoxylated monomer units in the polyoxyalkylene chains, or 0.02:1 to 20:1 molar based on the moles of the polyalkoxylate (i) e.g. 0.1:1 to 5:1. The initiator may coirprise a peroxy coitpound. Where the reagents (i) and (ii) are fully soluble we prefer to use an inorganic initiator especially hydrogen peroxide, or, less preferably a persulphate or percarbonate. Where the reagent (i) is sparingly soluble we prefer to use an organic initiator e.g. one which is soluble in reagent (i) such as an organic hydroperoxide or peroxide. The organic hydroperoxide or peroxide based initiator is preferably tertiary butyl perbenzoate. It may alternatively be, for example, tertiary butyl monopermaleate, di(tertiary butyl) peroxide, dilauroyl peroxide, tertiary butyl hydroperoxide, tertiary butylperoxy benzoate, or tertiary butyl peroxy-2-ethylhexanoate. It may also be possible in some cases to initiate the reaction photochemically e.g. using ultra violet or other energetic radiation or to use irradiation in conjunction with a chemical source of free radicals. Water typically constitutes 20-80% preferably 30-70% by weight of the total weight of the reaction medium. The presence of water miscible solvents in the reaction medium is not normally necessary or desirable but may be advantageous where the solubility of the reagent (i) is low or the medium is unduly viscous. Water miscible mono or polyhdyric alcohols such as methanol, ethanol, isopropanol, ethylene glycol, glycerol, or propylene glycol, may for example be used in small amounts e.g. up to 10% by weight of the reaction mixture. In general glycol ether solvents will constitute part of the reagent (i) and should not be added unless so required. The pH of the reaction medium is typically in the range pH 5-10, preferably above 5.5, e.g. pH 6-9.5 especially 6.5 to 9. Reaction times may typically be from 0.1 to 48 hours, preferably 2 to 26 hours, such as 7 to 31 hours, e.g. 10 to 20 hours, dependent upon teπperature and reagents employed. The reaction teπperature may, if the initiator is sufficiently active, be ambient but is preferably elevated, e.g. 60 to 280 C. The reaction may be carried out under reflux or under pressure in an autoclave, and the teπperature maintained until the reaction is substantially complete. The ether polycarboxylates or poly sulphonates may be added to water systems such as cooling water, industrial process water, boiler water, or water used in the hydrostatic testing of pipelines, oil well injection, central heating systems, automobile radiators or other aqueous systems liable to cause corrosion of metal surfaces. The ether polycarboxylate or poly sulphonate may be added in threshold amounts, e.g. 10 to 150 pp preferably 20 to 100 pp , especially 30 to 75 ppm. The ether polycarboxylate or polysulphonate may be used in conjunction with other water treatment agents, including: scale inhibitors; one or more other corrosion inhibitors especially phosphono carboxylic acids such as phosphonosuccinic acid, l-phosphono-l-2,3,4-tetracarboxy butane and their higher teleomers, or phosphorates such as acetodiphosphonate, amino tris (methylene phophonate) , ethylenediamine tetrakis (methylenephosphonate) , diethylenetriamine pentakis (methylenephosphonate) , triethylenetetramine hexakis (methylenephosphonate) or higher members of the series of (n) ethylene (n + 1) amine (n + 2) ( ethylenephosphonates) , and/or polymaleic acid; oxygen scavengers such as alkyl hydroxyla ines; biocides such as quaternary phosphonium salts, e.g. tetrakis (hydroxymethyl) phosphonium salts, quaternary ammonium salts, e.g. dodecyl trimethyl ammonium salts or aldehydes such as formaldehyde or glutaraldehyde , dispersants such as polyacrylates or lignin sulphonates; pH controlling agents such as fatty amines; oxidising agents such as ozone, hydrogen peroxide, chlorine or chlorine dioxide; coagulents; flocculating agents and/or freezing point depressants such as ethylene glycol. The ether polycarboxylates or poly sulphonates may be dissolved or dispersed in an anti-corrosive paint, varnish, enamel, lacquer, or other coating formulation. The formulation may comprise a volatile liquid vehicle, such as water or a volatile organic solvent including petroleum spirit, turpentine, ketones, esters and/or aromatic hydrocarbon solvent, and/or a drying oil, such as linseed oil, soya oil, tung oil or dehydrated castor oil, which may optionally be dissolved in said organic solvent or emulsified in said water. The formulation typically may also comprise a resin, e.g. a polyester, urea formaldehyde, melamine, acrylic, alkyd, polyurethane, vinyl chloride, vinyl acetate, phenolic or epoxy resin dissolved or dispersed therein and/or a dispersed pigment. We prefer that the pigment should be or should comprise a corrosion inhibiting pigment such as red lead, potassium zinc chromate, metallic zinc or aluminium powder or zinc oxide and/or that the formulation should contain one or more of the other corrosion inhibitors referred to above in addition to the ether polycarboxylate or poly sulphonate. The coating compositions may additionally contain any of the conventional paint ingredients, including pigments such as titanium oxide, iron oxide, carbon black, phthalocyanine pigments or aluminium stearate, chlorinated rubber, polystyrene, silicone, asphalt, wetting agents, dispersants, emulsifiers, biocides, marine antifoulants, antifoams, viscosifiers, fire retardants, fluorescers, aerosol propellants, talc, clay and/or plasticisers. Alternatively the ether poly carboxylate or poly sulphonate may be used to provide a corrosion inhibiting treatment for metal surfaces after any machining and prior to storage, coating, electroplating, polishing or ethching. Typically the work is coated with an aqueous solution containing at least an operative amount of said ether polycarboxylate or poly sulphonate e.g. 10 to 500 ppm preferably 25 to 300. e.g. 20 to 200 especially 25 to 100, more especially 30 to 80ppm. After contacting with the corrosion inhibiting solution the work may be rinsed and/or subjected to one or more coating of finishing operations such as resin coating, lacquering, enamelling, painting, electrophoretic coating, spattering, vapour deposition, electrodeposition, etching chemical or electrical polishing or may be put aside for storage. The work may be greased for storage, but an advantage of the treatment is that greasing and hence subsequent degreasing may be avoided. The ether poly sulphonates are novel compounds and constitute a further aspect of the present invention. The invention will be illustrated by the following example :- An ether polycarboxylate was prepared as follows:- The Manufacture of C - (Alkyl Ether Polycai±oxylate) Ethoxylated C alcohol (3B0) (lll.lg, o.3mol) and distilled water (80g) were dexoygenated by passing N through the mixture for 1 hour at 50°C. The deoxygenated mixture was heated to reflux temperature. To the refluxing mixture over a period of 5 hours an aqueous solution of maleic acid (104.5g, 0.9mol) and sodium hydroxide (72.2g, 0.3mol) was added in 3 aliquots. Three of a total of five aliquots of an aqueous solution of tertiary butyl perbenzoate (41.7g, 0.2mol) were added simultaneously with the acid/hydroxide aliquots. The remaining 2 aliquots of initiator were added over a further 10 hours. After a total refluxation time of 23 hours, a further addition of tertiary butyl perbenzoate was made (25g, 0.13mol) and the reaction allowed to continue until the total reaction time had reached 31 hours. The product was added to three portions of South Staffordshire water adjusted to pH 5.5, 7.0 and 8.5 respectively with sulphuric acid/sodium hydroxide, at a concentration of 50 ppm. Corrosion was measured by the linear polarisation method 3 as described in EP-A-0 491391 Pp 8 and 9. Results were as follows :- I WF. I pH Corrosicn (mils/yr.) 5.5 1.2 7.0 0.2 8.5 1.0 These corrosion rates are low compared with known inhibitors and effective protection extends over a very wide pH range. Example 2 The corrosion inhibitor of Exanple 1 was tested at various concentrations and at medium and high pH in South Staffordshire (hard) water in a linear polarisation test as indicated in Table II below: The inhibitor was dosed as solid. TABLE H pti ppm inhibitor Corrosion Rate nm/yr 7.5 blank 0.0470 7.5 10 0.0146 7.5 20 0.0051 7.5 50 0.0056 9.5 blank 0.2203 9.5 10 0.1781 9.5 20 0.0945 9.5 50 0.0322 Example 3 The corrosion inhibitor of exanple 1 was tested in two different types of water, South Staffordshire (hard) and Ennerdale (soft) in a coupon test. The test was carried out at 25°C for 3.98 days using a simple 4 x 0.5 inch mild steel coupon in each cell and changing the test solution daily. The inhibitor was dosed as solids and coupons were weighed at the beginning a d end of test and the weight loss was converted into mm/yr. the results are shown in Table III and an analysis of the water used in these examples is given in Table IV. TABLE HI Vfater PH Inhibitor Oαrrosion Rate ppm Solids πm/yr Ennerdale 7.5 Blank 0.561 Ennerdale 7.5 10 0.023 Ennerdale 7.5 20 0.005 Ennerdale 7.5 50 0.001 Ennerdale 9.5 Blank 0.681 Ennerdale 9.5 10 0.054 Ennerdale 9.5 20 0.009 Ennerdale 9.5 50 0.003 S.Staffs 7.5 Blank 0.551 S.Staffs 7.5 10 0.500 S.Staffs 7.5 20 0.272 S.Staffs 7.5 50 0.009 S.Staffs 9.5 Blank 0.419 S.Staffs 9.5 10 0.412 S.Staffs 9.5 20 0.398 S.Staffs 9.5 50 0.102 TABLE IV Parameter BTnerdale S. Staffs Total Hardness / ppm CaCCβ 13.5 163 Calcium Hardness / ppm Ca003 9.0 127 Alkalinity / ppm CaC03 11.0 93 Chloride / ppm Cl- 10.7 46 PH 7.5 7.4 Langelier Index -2.2 ' -0.4 Exanple 4 (i) A solution of 20% by wt of the ether carboxylate of exanple 1 in water is added over 1 hour at 50°C to a εtoichiometric amount of a stirred solution of zinc sulphate octahydrate in water. The white precipitate is filtered washed and vacuum dried. (ii) The preparation of (i) is repeated using a stirred suspension of calcium oxide in place of zinc sulphate. (iii) The preparation of (i) is repeated using barium hydroxide octahydrate in place of zinc sulphate. (iv) The preparation of (i) is repeated using aluminium sulphate hexadecahydrate in place of zinc sulphate. Exanple 5 The products of example 4 are each suspended in a short oil alkyd resin primer having the formulation carbon black 2.0g anti-corrosive pigment 5.4g calcium carbonate 30.Og alkyd resin 38.Og xylene 20.Og cobalt octoate (10% Co) 0.2g in each case the formulation gives enhances corrosion protection coπpared with a blank containing no anti-corrosive pigment.

Claims: KL058 - CLAIMS 1. The use of ether polycarboxylic or polysulphonic acids and their salts as corrosion inhibitors in water treatment. 2. A method of treating aqueous systems liable to give rise to problems of corroding metal surfaces, which comprises adding thereto threshold levels of an ether polycarboxylic or polysulphonic acid or its water soluble salts. 3. The use of ether polycarboxylates or polysulphonates in anticorrosive coating conpositions. 4. An anticorrosive coating formulation comprising: a liquid vehicle coπprising water, a volatile organic solvent and/or a drying oil; a binder which comprises said drying oil and/or a resin dissolved or dispersed in said liquid vehicle; corrosion inhibitor dissolved or dispersed in said liquid vehicle; and optionally a pigment or dye dispersed or dissolved in said liquid vehicle; characterised in that said corrosion inhibitor comprises an ether polycarboxylate or polysulphonate. 5. The use of ether polycarboxylates or polysulphonates to treat metal surfaces prior to coating or metal finishing operations or to storage. 6. A method for the treatment of metal surfaces which comprises :- contacting said surfaces with an aqueous solution of an ether polycarboxylate or polysulphonate and subsequently subjecting said surfaces to at least one coating or metal finishing operation, greasing and/or storage. 7. An anticorrosive pigment comprising a polyvalent metal salt of an ether polycarboxylic acid or polysulphonic acid. 8. A coating composition having a polyvalent metal salt of an ether polycarboxylate suspended or dispersed therein. 9. A method according to either of claims 1 and 6 wherein said ether polycarboxylate or polysulphate has the formula 2 3 R(R X ) X R (R ) Z H R 4 y in which R is a straight or branched chain alkyl, alkaryl or alkenyl group or straight or branched chain alkyl or alkenyl carboxy group, having, in each case, up to 27 carbon atoms, or hydrogen, each R is 2 . an OCH CH or an 0CH(CH )CH group, each R is an OC H or OC H group, each R is a C(R ) C(R ) group, wherein from 1 to 4 R groups 3 5 per R group are CO A and/or SO A groups, each other R group being a C -C alkyl, hydroxy alkyl or carboxyalkyl group or, R 4 i.s OH, SO A, 6 7 6 SO A, OR, sulphosuccinyl, OCH CO A, or R NR , R is a C -C alkyl or hydroxyalkyl group, R is a C alkyl group, a benzyl group, a CH CO A, -> 0 or PO.A group, A is a cation capable of forming water soluble salts of said carboxylic acid, each z is from 1 to 5, y is at least 1 and (x+y) has an average value of from 1 to 50, wherein tthhee RR 1 1 aanndd RR22 ggrroouuppss mmaayy be arranged randomly or m any order along the polyalkoxylate chain. 10. A method according to claim 9 wherein said polycarboxylate is a poly(carboxyalkylated) alkyl polyethoxylate.

Inventors: DAVIS KEITH PHILIP, SMITH ALAN CRAIG, WILLIAMS MICHAEL JOHN, DAVIS, KEITH, PHILIP, SMITH, ALAN, CRAIG, WILLIAMS, MICHAEL, JOHN
Applicants: ALBRIGHT & WILSON, DAVIS KEITH PHILIP, SMITH ALAN CRAIG, WILLIAMS MICHAEL JOHN, ALBRIGHT & WILSON LIMITED, DAVIS, KEITH, PHILIP, SMITH, ALAN, CRAIG, WILLIAMS, MICHAEL, JOHN
Application year: 1994
Main classification: C23F11
IPC codes: C09D5, C23F11